Quiz1d2o9nyf4hwsci4.cloudfront.net/2013/fall/quizzes/1/quiz1.pdf · This%is%CS50.%...

This%is%CS50.%Harvard*University*Fall%2013*

%%

0%<%18%

Quiz*1*out*of*94*points*

*Print*your*name*on*the*line*below.*

%% % % % % % % % % % %

%

Do%not%turn%this%page%over%until%told%by%the%staff%to%do%so.%%

This%quiz%is%"closedBbook."%%However,%you%may%utilize%during%the%quiz%one%twoBsided%%page%(8.5"%×%11")%of%notes,%typed%or%written,%and%a%pen%or%pencil,%nothing%else.%

%

Scrap%paper%is%included%at%this%document's%end.%Unless%otherwise%noted,%you%may%call%any%functions%we've%encountered%this%term%in%code%that%you%write.%

You%needn't%comment%code%that%you%write,%but%comments%may%help%in%cases%of%partial%credit.%If%running%short%on%time,%you%may%resort%to%pseudocode%for%potential%partial%credit.%

*

Circle*your*teaching*fellow's*name.*Alisa%Nguyen%

Allison%%BuchholtzBAu%

Angela%Li%

Armaghan%Behlum%

Ben%Shryock%

Bo%Ning%Han%

Casey%Grun%

Chi%Zeng%

Christopher%Bartholomew%

Chris%Mueller%

Cynthia%Meng%

Dan%Bradley%

Daven%Farnham%

David%Kaufman%

%

%

Dianna%Hu%

Doug%Lloyd%

Ed%Hebert%

Gabriel%Guimaraes%

George%Wu%

Hannah%Blumberg%

Ian%Nightingale%

Jackson%Steinkamp%

Jared%Pochtar%

Jason%Hirschhorn%

Joe%McCormick%

Jonathan%Marks%

Jonathan%Miller%

Jordan%Jozwiak%

Joseph%Ong%

%

%

Julian%Salazar%

Karen%Xiao%

Katryna%Cadle%

Keenan%Monks%

Kendall%Sherman%

Kevin%Mu%

Kevin%Schmid%

Levi%Roth%

Lucas%Freitas%

Luciano%Arango%

Lucy%Cheng%

Lydia%Chen%

Marshall%Zhang%

Mike%Rizzo%

Patrick%Schmid%

%

R.J.%Aquino%

Rebecca%Chen%

Rhed%Shi%

Rob%Bowden%

Roger%Zurawicki%

Saheela%Ibraheem%

Sharon%Zhou%

Tim%McLaughlin%

Tomas%Reimers%

Travis%Downs%

Tyler%Morrison%

Varun%Sriram%

Wesley%Chen%

William%Hakim%

William%Xiao%

Zamyla%Chan


1%<%18%

%

%%%%%

**

for*staff*use*only*!

final!score!out!of!94!


2%<%18%

Getting*Strings.*%

Consider%three%different%versions%of%a%program,%below,%each%of%which%is%intended%to%get%and%print%a%string%

from%a%user.%

* // version 1 #include <stdio.h> int main(void) { char* s; scanf("%s", s); printf("%s\n", s); }%

// version 2 #include <stdio.h> int main(void) { char s[50]; scanf("%s", s); printf("%s\n", s); }

// version 3 #include <stdio.h> #include <stdlib.h> int main(void) { char* s = malloc(50); scanf("%s", s); printf("%s\n", s); free(s); }

%

0.% (2%points.)%%Suppose%that%version%1%is%compiled%and%executed.%%Why%might%the%program%segfault?%

%

%

%

%

%


%

%

%

%

%

%


%

%

%

%

%

%

3.% (2%points.)%%With%respect%to%the%programs'%use%of%memory,%how%do%version%2%and%version%3%differ?%

%

%

%

% for*staff*use*only*%

%%

%—*%

%

%


3%<%18%

Small*Bytes.*%

4.% (5%points.)%%Consider%the%types%below.%

%typedef char* string; typedef struct node { int n; struct node* next; } node; typedef struct { char* name; char* house; } student;

%

% Complete%the%table%below%by%recording%to%the%right%of%each%type%its%size%in%bytes%(not%bits).%%Assume%

a%32Mbit%architecture%like%the%CS50%Appliance.%%

%

type* bytes*

node %

node* %

string %

struct node* %

student %

%

%

%

for*staff*use*only*%

%%

%—*%

%

%


4%<%18%

HTTP/1.1.%%

For%each%of%the%HTTP%status%codes%below,%explain,%in%no%more%than%three%sentences,%why%a%server%might%

respond%with%that%code.%

%

%

5.% (2%points.)%%200 OK%%

%

%

%

%

%

6.% (2%points.)%%302 Found%%

%

%

%

%

%

7.% (2%points.)%%403 Forbidden%%

%

%

%

%

%

8.% (2%points.)%%404 Not Found%%

%

%

%

%

%

9.% (0%points.)%%418 I'm a teapot%%

%

%

%

%

%

10.% (2%points.)%%500 Internal Server Error%* for*staff*use*only*

%

%%

%—*%

%

%


5%<%18%

Double*Trouble.*%

Consider%the%program%below,%wherein%list%is%an%unsorted%doublyMlinked%list%of%integers.%%#include <stdbool.h> #include <stdlib.h> typedef struct node { int n; struct node* prev; struct node* next; } node; node* list = NULL; void insert(int n); void remove(int n); int main(void) { insert(50); insert(34); insert(59); insert(20); insert(106); insert(36); insert(52); remove(50); }

11.% (4% points.)% % Complete% the% implementation%of%insert% below% in% such% a%way% that% it% inserts%n% into%

list%in%constant%time%(even%if%already%present).%

% void insert(int n) { %

%

%

%

%


%%

%—*%

%

%


6%<%18%

12.% (6%points.)%%Complete%the%implementation%of%remove%below%in%such%a%way%that%it%removes%n%from%

list% in% linear% time.% % You%may%assume% that%n,% if% present% in%list,%will% be%present%no%more% than%

once.%

% void remove(int n) { %

%

%

%

%

%

%

%

%

%

%

***********%

13.% (2%points.)% % Suppose% that%execution%of% the%program% is%paused%after% all% statements% in%main% have%executed,% per% the% prescribed% implementations% of% insert% and% remove,% but% before% main%%returns% (i.e.,% exits).% % Complete% the% drawing% below% in% such% a% way% that% it% depicts% the% unsorted%

doublyMlinked%list%that%exists%in%memory%at%that%moment%in%time.%

*


%%

%—*%

%

%


7%<%18%

World*Wide*What.%*14.% (6%points.)% %Suppose%that%a%user%types%https://www.facebook.com/% into%his%or%her%browser's%

address% bar% and% then% hits% Enter% (after% clearing% any% cookies).% % Explain,% in% a% short% paragraph,% the%

process%by%which%Facebook's%home%page% is% retrieved,%using%each%of% the%six% terms%below%at% least%

once%in%your%explanation%in%such%a%way%that%your%understanding%of%each%is%clear.%%Underline%every%

instance%of%each%term%in%your%paragraph.%

%

DNS%%⋅%%HTML%%⋅%%HTTP%%⋅%%IP%address%%⋅%%port%%⋅%%router%%

****************Quadded.**15.% (2%points.)%%Consider%the%PHP%array%below.%

% $quad = ["Cabot House", "Currier House", "Pforzheimer House"]; %

% Complete%the%code%fragment%below%in%such%a%way%that%it%outputs%an%unordered%(i.e.,%bulleted)%list%

of%houses%by%iterating%over%$quad.%%Assume%that%$quad%is%in%scope.%%Take%care%to%close%the%ul%tag%that%we've%opened%for%you,%but%no%need%to%add%elements%like%html,%head,%or%body.%%Recall%that%ul%elements%have%li%(i.e.,%list%item)%elements%as%children.%

% <ul> <?php


%%

%—*%

%

%


8%<%18%

Tradeoffs.**(2*points*each.)%%

For%each%of%the%design%decisions%below,%explain%one%upside%and%one%downside,%each%in%no%more%than%two%

sentences.%

%

16.% Validating%users'%input%clientMside%(as%with%JavaScript)%instead%of%serverMside%(as%with%PHP).%

%

! upside:!%

%

! downside:!!%

17.% Using%a%linked%list%instead%of%an%array%to%maintain%a%sorted%list%of%integers.%

%

! upside:!%

%

! downside:!!%

18.% Using%PHP%instead%of%C%to%write%a%commandMline%program.%

%

! upside:!%

%

! downside:!!%

19.% Using%a%SQL%database%instead%of%CSV%file%to%store%data.%

%

! upside:!%

%

! downside:!!%

20.% Using%a%trie%instead%of%a%hash%table%with%separate%chaining%to%store%a%dictionary%of%words.%

%

! upside:!%

%

! downside:%%


%%

%—*%

%

%


9%<%18%

DOM,*DOM*DOM*DOM.*%

21.% (4%points.)%%Consider%the%HTML%below.%

%<!DOCTYPE html> <html> <head> <title>quiz</title> </head> <body> <div>top</div> <div>middle</div> <div>bottom</div> </body> </html> %

Complete%the%DOM%below%in%such%a%way%that%it%represents%the%HTML%above,%using%any%shape(s)%for%

nodes.%

%%

%


%%

%—*%

%

%


10%<%18%

Attack!*%

Recall%the%program%below.%

%#include <string.h> void foo(char* bar) { char c[12]; memcpy(c, bar, strlen(bar)); } int main(int argc, char* argv[]) { foo(argv[1]); } %

22.% (2%points.)%%How%might%an%adversary%"trick"%this%program%into%executing%arbitrary%code?%

%

%

%

%

%

23.% (3%points.)% %Complete%the%reMimplementation%of%foo%below%in%such%a%way%that%the%program%is%no%

longer%vulnerable%to%that%attack.%%Any%approach%that%prevents%the%attack%is%acceptable.%

% void foo(char* bar) { %

%

%


%%

%—*%

%

%


11%<%18%

Itsa*Mario*again?*%

24.% (4% points.)% % Toward% the% end% of% World% 2M3% in% Nintendo's% Super% Mario% Brothers% 3,% Mario% must%

descend%a%"halfMpyramid"%of%blocks%(unless%he%flies%over%it).%%Below%is%a%screenshot.%

%

% %%

% Complete% the% implementation% of% the% commandMline% PHP% program% below% in% such% a% way% that% it%

recreates%this%particular%halfMpyramid%using%hashes%(#)%for%blocks.%%No%need%for%user%input;%you%may%

hardMcode%the%halfMpyramid's%height%(7)%into%your%program.%

%#!/bin/env php <?php

*


%%

%—*%

%

%


12%<%18%

woof*am*back.*%

25.% (4%points.)% %Complete%the% implementation%of%the%web%page%

below%in%such%a%way%that%if%someone%visits%the%page,%inputs%

his% or% her% name,% and% then% submits% the% form,% he% or% she% is%

greeted%via%a%call%to%alert%with%a%window%like%that%at%right.%%If%a%user% fails% to% input%a%name%before%submitting% the% form,%

no%alert%should%appear.%%You%are%welcome,%but%not%required,%

to%use%jQuery%functions.%%%

%<!DOCTYPE html> <html> <head> <script src="http://code.jquery.com/jquery-latest.min.js"></script> <script> </script> <title>quiz</title> </head> <body> <form id="inputs"> <input id="name" type="text"/> <input id="button" type="submit" value="Greet"/> </form> </body> </html>


%%

%—*%

%

%


13%<%18%

MyOhMySQL.*%

Suppose% that% a% bank% relies% on% a% SQL% table% called% accounts% to% store% customers'% accounts,% wherein%

number% (the% table's% PRIMARY% key)% represents% a% user's% 12Mdigit% account% number,% and% balance%represents% how% much% money% the% customer% has% in% his% or% her% account,% per% the% (incomplete)% schema%

below.%%As%per%the%default%value%of%100.00%for%balance,%the%bank%gives%customers%$100%anytime%they%

open%an%account.%

%

%%

26.% (2% points.)% % Complete% the% schema% for% accounts% above% by% specifying,% next% to% number% and%balance%on%the%schema%itself,%an%appropriate%SQL%type%for%each.%

%

%

27.% (2% points.)% % Suppose% that% the% bank% imposes% a% $20% "monthly%maintenance% fee"% on% all% accounts.%%

With%what%SQL%query% could% the%bank%deduct%$20% from%every%account% (even% if% it% results% in% some%

negative%balances)?%

%

%

%

%

%

%

28.% (2% points.)% % With% what% SQL% query% could% the% bank% retrieve% the% account% numbers% of% its% richest%

customers,%those%with%balances%greater%than%$1,000?%

*****%

29.% (2% points.)% % With% what% SQL% query% could% the% bank% close% (i.e.,% delete)% every% account% that% has% a%

balance%of%$0?%

*


%%

%—*%

%

%


14%<%18%

Queue*Guide.*%

Suppose%that%a%queue%for%(nonMnegative)%integers%is%defined%per%the%below,%wherein%CAPACITY%(a%global%constant)%is%the%maximum%number%of%integers%that%can%be%in%the%queue,%size%is%the%number%of%integers%

currently%in%the%queue,%and%front%is%the%index%of%the%front%of%(i.e.,%first%integer%in)%the%queue.%%

typedef struct { int numbers[CAPACITY]; int front; int size; } queue; %

Assume%that%a%queue%has%been%declared%globally%with%%%

queue q; %

and%that%q%has%been%initialized%for%you%(e.g.,%in%main)%per%the%below.%%

q.front = 0; q.size = 0; %

30.% (4% points.)% % Complete% the% implementation% of% enqueue% below% in% such% a% way% that% the% function%%adds%n% to%(the%end%of)%q%and%then%returns%true.% % If%q% is% full%or%n% is%negative,%the%function%should%instead%return%false.%%Assume%that%bool%as%well%as%true%and%false%have%been%declared%for%you%(as%via%cs50.h%or%stdbool.h).%

% bool enqueue(int n) { *******31.% (4% points.)% % Complete% the% implementation% of% dequeue% below% in% such% a% way% that% the% function%

dequeues%(i.e.,%removes%and%returns)%the%int%at%the%front%of%q.%%(To%remove%the%int,%it%suffices%to%"forget"%it;%you%needn't%overwrite%its%bits.)%%If%q%is%empty,%the%function%should%instead%return%-1.%

%int dequeue(void) {

*


%%

%—*%

%

%


15%<%18%

Pssst,*BST.*%

Recall%that%a%binary%search%tree%(BST)%is%a%binary%tree%(each%of%whose%nodes%thus%has%0,%1,%or%2%children),%

the%value%of%whose%root% is:%greater%than%that%of% its% left%child,% if%any,%and%any%descendants%thereof;%and%

less% than%that%of% its% right%child,% if%any,%and%any%descendants% thereof.% %Moreover,%each%child% is% the%root%

of%a%BST.%

%

32.% (2%points.)%%Consider%the%binary%tree%below%whose%nodes%do%not%yet%have%values.%%% %

%%

% Insert%the%six%integers%below%into%that%tree,%as%by%writing%one%integer%in%each%circle,%in%such%a%way%

that%the%binary%tree%is%a%BST.%

%

34%%⋅%%59%%⋅%%20%%⋅%%106%%⋅%%36%%⋅%%52%%

%

33.% (2%points.)%%Complete%the%definition%of%node%below%in%such%a%way%that%it%represents%a%node%in%a%BST,%the%value%of%which%is%of%type%int.%%You%may%name%its%fields%however%you'd%like.%

% typedef struct node { } node; **%


%%

%—*%

%

%


16%<%18%

34.% (4%points.)%%Complete%the%implementation%of%traverse%below%in%such%a%way%that,%given%the%root%of%a% BST,% the% function% performs% an% "inMorder% traversal,"% printing% each% of% the% tree's% integers% with%

printf% from% smallest% to% largest,% one% per% line.% % Assume% that% node% is% defined% per% your% own%implementation%one%problem%ago.%%Do%not%assume%that%root%will%be%nonMNULL.%

%% void traverse(node* root) { ****************

****

*%

*


%%

%—*%

%

%


17%<%18%

Scrap*Paper.%*Nothing!on!this!page!will!be!examined!by!the!staff!unless!otherwise!directed.!

Quiz1d2o9nyf4hwsci4.cloudfront.net/2013/fall/quizzes/1/quiz1.pdf · This%is%CS50.%...

Documents

Transcript of Quiz1d2o9nyf4hwsci4.cloudfront.net/2013/fall/quizzes/1/quiz1.pdf · This%is%CS50.%...

Quiz*1*d2o9nyf4hwsci4.cloudfront.net/2013/fall/quizzes/1/quiz1.pdf · This%is%CS50.%...

Documents

Transcript of Quiz*1*d2o9nyf4hwsci4.cloudfront.net/2013/fall/quizzes/1/quiz1.pdf · This%is%CS50.%...

Quiz1d2o9nyf4hwsci4.cloudfront.net/2013/fall/quizzes/1/quiz1.pdf · This%is%CS50.%...

Transcript of Quiz1d2o9nyf4hwsci4.cloudfront.net/2013/fall/quizzes/1/quiz1.pdf · This%is%CS50.%...